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The experimental vaccine produced important signs of immune response in a small group of adults, a sign that it could potentially protect people against COVID-19, researchers reported May 22 online in The Lancet medical journal.
"These results represent an important milestone," researcher Wei Chen, part of a team with the Beijing Institute of Biotechnology, said in a journal news release.
"However, these results should be interpreted cautiously," Chen continued. "The challenges in the development of a COVD-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from COVID-19."
This causes the body to produce the "spike" protein that the coronavirus uses to invade human cells. In turn, the immune system responds to the presence of the protein by creating antibodies that potentially could fight off future coronavirus infections, the researchers said.
Within a month, most of the 108 healthy adult participants in the phase 1 trial had a fourfold increase in binding antibodies. These antibodies can bind to the coronavirus, but don't necessarily attack it.
Half of the participants who received low or moderate doses and three-quarters of those who received a high dose also developed neutralizing antibodies, which can protect the body against the coronavirus, researchers reported.
"Not only did the virus induce antibodies but also T-cell immunity, which will also be important for confirming protection," said Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security, who called the trial results "very welcome."
However, Adalja said the vaccine's use of a common cold virus to deliver its genetic payload could hamper its effectiveness.
"Adenoviruses are very common and there are many people with preexisting immunity," Adalja said. "In a prior trial using this type of platform for HIV vaccination, there was a paradoxical increase in risk of infection in those who are vaccinated who had preexisting adenovirus 5 immunity. Whether this phenomenon is present with this vaccine will be important to investigate in detail in phase 2 and phase 3 trials."
There was some evidence of this in the clinical trial, with people who had existing cold virus immunity showing a reduced immune response to the vaccine, the Chinese researchers noted.
A full-fledged phase 2 trial has been initiated in Wuhan to see if the results can be replicated in 500 healthy adults, which would include 250 volunteers given a moderate dose, and another 250 given either a low dose or a placebo.
The U.S. Department of Health and Human Services has entered a full-court press to develop potential COVID-19 vaccine candidates.
U.S. federal officials said Thursday the agency would provide up to $1.2 billion to the drug company AstraZeneca to develop a potential coronavirus vaccine from a lab at the University of Oxford in England.
The fourth, and largest, vaccine research agreement funds a clinical trial of the potential vaccine in the United States this summer with about 30,000 volunteers, the New York Times reported.
The goal? To make at least 300 million doses that could be available as early as October, the HHS said in a statement.
However, many experts have said that the earliest an effective, mass-produced vaccine would be available won't be until sometime next year, and billions of doses would be needed worldwide.
The United States has already agreed to provide up to $483 million to the biotech company Moderna and $500 million to Johnson & Johnson for their vaccine efforts. It is also providing $30 million to a virus vaccine effort led by the French company Sanofi, the Times reported.
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